1. Field of the Invention
This invention relates to earth boring bits adapted for carriage on the end of a drill string for drilling bore holes in the earth, and more particularly, to a rotary mining bit.
2. Brief Descripton of the Prior Arts
A number of mining bits have previously been proposed for use in mining minerals from the earth by rotating the bit while it is mounted at the end of an elongated drill string. A bit which is of this general type, and which has some similarity to the present invention, is described in McKenry et al U.S. Pat. No. 3,720,273 assigned to Kennametal, Inc. of Latrobe, Pa. This type of bit includes a bit body which can typically be a disc-shaped steel forging. On the upper or rear side of the solid bit body, a radially inwardly tapering neck or shank portion has its relatively larger end secured to the center of the body, and projects rearwardly therefrom.
This shank or neck portion carries external threads to facilitate connection of the bit to a tubular driving member, such as a drill string. A fluid passageway extends through the shank or neck portion and through the body and terminates in divergent ports so that fluid under pressure can be supplied to the working face of the bit to carry away from the working region, material chiseled from the bore hole by the bit.
On the opposite side of the body (the lower or forward side) from the externally threaded neck portion or shank, the body is provided with an internally threaded, axially extending bore which is axially aligned with the fluid passageway in the body. The bore receives the threaded neck portion of a pilot cutter.
The opposite side of the body from that from which the externally threaded tapered neck or shank extends may be termed the working face or cutting side of the body, and at circumferentially spaced locations thereabout, in line with the radially outer sides thereof, are a plurality of cutter support blocks. Typically there may be three or four of these cutter support blocks in a first, radially outermost group thereof, but there may be more. The cutter support blocks are mounted on the bit body so as to incline so that they lean in a circumferential direction with respect to the rotational axis of the bit, which direction of inclination is toward the direction of rotation of the bit.
Each of the cutter support blocks has a cutter element rotatably mounted therein. Each cutter element has a cylindrical shank which is disposed in a cylindrical bore formed in the respective cutter support block. The cutter elements are retained in their respective bores by means of resilient keeper rings, and can be easily removed and replaced when they become dulled. The several cutter support blocks are affixed to the bit body so that the cutters which are removably and rotatably carried in the several support blocks are inclined slightly outwardly in a radial direction, and also in the direction of rotation of the mining bit when it is in use. The cutter elements cooperate with the pilot cutter to accomplish efficient boring of a bore hole through an earthen formation.